A substrate cleaning apparatus for processing substrates, such as wafers, has a substrate holding device for holding and rotating a substrate. The substrate holding device is configured to hold a peripheral edge of a substrate with a plurality of chucks. While a wafer (or substrate) is held and rotated by the chucks, a cleaning tool, such as a roll sponge or a pen sponge, is brought into contact with a surface of the wafer in the presence of a cleaning liquid, thereby cleaning the surface of the wafer.
Wafers having a diameter of 300 mm are expected to be replaced with wafers having a diameter of 450 mm in the near future. However, the increase in wafer size may cause the following problems. When four equally-spaced chucks grip a wafer having a diameter of 450 mm, the wafer bends between adjacent two of the chucks and an amount of deflection reaches about 0.5 mm. This amount of deflection is about five times the amount of deflection when a wafer having a diameter of 300 mm is held by the four chucks. If the cleaning tool is pressed against the surface of the wafer that bends largely while it is in rotation, the cleaning tool does not uniformly contact the wafer and is unable to clean the surface of the wafer uniformly. Moreover, the contact with the cleaning tool may cause the wafer to further bend, and may possibly result in a crack in the wafer.
It is possible to reduce the amount of wafer deflection by using an increased number of chucks. However, the increase in the number of chucks may give rise to a new problem that a hand of a transfer robot is likely to contact the chucks when the transfer robot transports the wafer. Moreover, it is difficult to reduce the size of the hand and it is also difficult to provide a recess in the hand for making the hand stay clear of the chucks because it is necessary to ensure a mechanical strength of the hand that bears the weight of the wafer with a diameter of 450 mm.